SpitzerObservations ofz∼ 3 Lyman Break Galaxies: Stellar Masses and Mid‐Infrared Properties

We describe the spectral energy distributions (SEDs) of Lyman Break Galaxies(LBGs) at z~3 using deep mid-infrared and optical observations of the ExtendedGroth Strip, obtained with IRAC and MIPS on board Spitzer and from the ground,respectively. We focus on LBGs with detections at all four IRAC bands, inparticular the 26 galaxies with IRAC 8 micron band (rest--frame K-band)detections. We use stellar population synthesis models and probe the stellarcontent of these galaxies. Based on best--fit continuous star-formation modelswe derive estimates of the stellar mass for these LBGs. As in previous studies,we find that a fraction of LBGs have very red colors and large estimatedstellar masses (M_stellar > 5 x 10 ^{10} M_solar): the present Spitzer dataallow us, for the first time, to study these massive LBGs in detail. We discussthe link between these LBGs and submm-luminous galaxies.We find that the numberdensity of these massive LBGs at high redshift is higher than predicted bycurrent semi-analytic models of galaxy evolution.Comment: accepted for publication by Astrophysical Journa